Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$24.62	10.125%	$27.1128	$27.11	$27.10	$27.10
Purchase #2	$11.32	11.365%	$12.6065	$12.61	$12.60	$12.60
Purchase #3	$76.46	11.465%	$85.2261	$85.23	$85.25	$85.20
Purchase #4	$75.48	3.506%	$78.1263	$78.13	$78.15	$78.10
Purchase #5	$104.55	10.246%	$115.2622	$115.26	$115.25	$115.30
Purchase #6	$186.87	7.104%	$200.1452	$200.15	$200.15	$200.10
Purchase #7	$126.26	10.656%	$139.7143	$139.71	$139.70	$139.70
7 purchase totals =	$605.56		$658.1934	$658.20	$658.20	$658.10